Suzaku mapped iron, magnesium, silicon and sulfur in four directions all across the Virgo galaxy cluster for the first time. The northern arm of the survey (top) extends 5 million light-years from M87 (center), the massive galaxy at the cluster’s heart. Ratios of these elements are constant throughout the cluster, which means they were mixed well early in cosmic history. The dashed circle shows what astronomers call the virial radius, the boundary where gas clouds are just entering the cluster. Some prominent members of the cluster are labeled as well. The background image is part of the all-sky X-ray survey acquired by the German ROSAT satellite. The blue box at center indicates the area shown in the visible light image. Credit: A. Simionescu (JAXA) and Hans Boehringer (MPE)
A new survey of hot, Xray-emitting gas in the Virgo galaxy cluster shows that the elements needed to make stars, planets and people were evenly distributed across millions of light-years early in cosmic history, more than 10 billion years ago.
The Virgo cluster, 54 million light-years away, is the nearest galaxy cluster and the second brightest in X-rays. The cluster is home to >2,000 galaxies, and the space between them is filled with a diffuse gas so hot it glows in X-rays. Using Japan’s Suzaku X-ray satellite, a team led by Aurora Simionescu at JAXA, acquired observations of the cluster along four arms extending up to 5 million light-years from its center.
“Heavier chemical elements from carbon on up are produced and distributed into interstellar space by stars that explode as supernovae at the ends of their lifetimes,” Simionescu said. This chemical dispersal continues at progressively larger scales through other mechanisms, such as galactic outflows, interactions and mergers with neighboring galaxies, and stripping caused by a galaxy’s motion through the hot gas filling galaxy clusters.
Supernovae fall into 2 broad classes. Stars born with >8X sun’s mass collapse under their own weight and explode as core-collapse supernovae. White dwarf stars may become unstable due to interactions with a nearby star and explode as so-called Type Ia supernovae. These different classes of supernovae produce different chemical compositions. Core-collapse supernovae mostly scatter elements ranging from oxygen to silicon, while white dwarf explosions release predominantly heavier elements, such as iron and nickel. Surveying the distribution of these elements over a vast volume of space, such as a galaxy cluster, helps astronomers reconstruct how, when, and where they were produced. Once the chemical elements made by supernovae are scattered and mixed into interstellar space, they become incorporated into later generations of stars.
The overall composition of a large volume of space depends on the mix of supernova types contributing to it. Eg accounting for the overall chemical makeup of the sun and solar system requires a mix of roughly one Type Ia supernova for every 5 core-collapse explosions.
In an earlier study led by Werner, Suzaku data showed that iron was distributed uniformly throughout the Perseus Galaxy Cluster, but information about lighter elements mainly produced by core-collapse supernovae was unavailable. The Virgo Cluster observations supply the missing ingredients. Simionescu et al detect iron, magnesium, silicon and sulfur all the way across a galaxy cluster for the first time. The elemental ratios are constant throughout the entire volume of the cluster and roughly consistent with the composition of the sun and most of the stars in our own galaxy.
The same ratio of supernova types – the same recipe – thought to be responsible for the solar system’s makeup was at work throughout the universe. This likely happened when the universe was between 2 and 4 billion years old, a period when stars were being formed at the fastest rate in cosmic history. “In other words, the chemical requirements for life are common throughout the cosmos.” http://www.nasa.gov/feature/goddard/suzaku-finds-common-chemical-makeup-at-largest-cosmic-scales
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